Yeah, I think that's why they revisited the idea in PC3 and PC4, since it didn't seem to really be all that balanced. PC2 was a change from PC1, which only had monster PCs attack at their current HD, and thus they plateaued at a certain point (some much earlier than others, and some would be much more well off at early levels due to high HD). It seems to be one of the mechanics of the PC Race notion that was very much in flux, whereas most of the other areas (xp progression and calculation, HD and maximum HD) remained more or less stable across the board.BillionSix wrote:In PC2, it says that upon reaching 8th level (or the maximum HD level) the PC's fight and use saving throws based on either their HD or their character level, whichever is more advantageous.
In absence of another sort of mechanic (that I don't have any ideas for myself), I'd probably go with the more recent/later developed idea of progression as monster HD until no HD gained any longer, then +1 every 2 levels. It still isn't necessarily all that balanced (obviously, higher HD monsters will benefit the most, though they also suffer the worst xp costs), but it at least provides some measure of incremental advancement, whereas the others are either a little too much, or else none at all.